Prosthetic heart valve

ABSTRACT

A bileaflet heart valve incorporates a pivot arrangement that minimizes resistance to downstream blood flow in the open position yet has prompt response and therefore minimal regurgitation upon flow reversal. A valve body having an axially curved entrance that smoothly joins a generally cylindrical body of extended axial length provides excellent fluid flow characteristics when combined with leaflets that can assume orientations perfectly aligned with the downstream flow of blood. Identical flat leaflets can assume a parallel orientation in the fully open position during downstream blood flow or can assume other low energy positions. Flat ears, which extend laterally from opposite surfaces of the leaflets, interengage with cavities of unique design having upstream and downstream lobes separated by an intermediate throat portion defined by inward and outward fulcrums. The downstream lobes may be designed to facilitate movement to the parallel orientation or to cause the leaflets to optionally prerotate toward the closed position. As soon as reverse flow begins, upstream displacement of the leaflets causes the ears to contact straight camming surfaces located upstream of the outward fulcrums which, in combination with the fulcrums and a downwardly directed, concave surface at the upstream end of the upstream lobe, positively guide each leaflet through efficient closing which ends in substantially rotational movement. A pyrocarbon valve body receives suture rings that permit the tissue annulus to directly contact an exterior surface region of the valve body.

This application is a continuation-in-part of our earlier applicationSer. Nos. 08/441,791, now U.S. Pat. No. 5,545,216, and 08/441,809,pending, both filed May 16, 1995.

FIELD OF THE INVENTION

The present invention relates to mechanical heart valve prostheses and,in particular, to improved prosthetic heart valves having pairs of valvemembers or occluders which both pivot and translate in moving betweentheir open and closed positions.

BACKGROUND OF THE INVENTION

A wide variety of heart valve prostheses have been developed whichoperate hemodynamically, in conjunction with the pumping action of theheart, to take the place of a defective natural valve. These valves havegenerally been designed to function with valve members in the form of asingle occluder, a pair of occluders or leaflets or even three or moreoccluders; such occluders pivot along eccentric axes (or both pivot andtranslate) to open and close a central blood flow passageway through agenerally annular valve body within which the occluders are usuallyappropriately supported.

U.S. Pat. No. 4,451,937 (Jun. 5, 1984) discloses an early heart valvedesign wherein arcuate depressions in flat sidewall sections of a Valvebody guide valve members having ears extending from their lateral edgesthat are received in such depressions.

U.S. Pat. No. 4,689,046 (Aug. 25, 1987) discloses a bileaflet heartvalve having a pair of flat leaflets with ears of generally trapezoidalconfiguration extending from the flat lateral surfaces thereof. The earshave flat end faces and are received in diametrically opposed recessesin the valve body having facing flat end surfaces; the recesses areshaped so that the ears are rockingly engaged therein by tapered recessguide wall surfaces of arcuate configuration.

U.S. Pat. No. 5,123,920 (Jun. 23, 1992) discloses a bileaflet heartvalve having curved leaflets with bulbous downstream sections having apivot construction wherein notches are formed in the outflow surfaces ofthickened portions of the pair of leaflets, which notches engagecomplementary surfaces on pivot projections that extend radially inwardfrom diametrically opposite locations on the valve body sidewall.

U.S. Pat. No. 5,137,532 (Aug. 11, 1992) discloses bileaflet heart valveshaving pivot arrangements which allow the leaflets to assume anorientation substantially parallel to the centerline through the valvein their open position in a valve body which is elongated in axiallength relative to bileaflet valves of earlier design wherein designersgenerally attempted to minimize the length of the blood flow paththrough the valve body, because the valve was felt to be confining. Inone embodiment, camming surfaces provided on the leaflets engageappropriately located projections extending radially inward from thevalve body sidewall, and the upstream displacement of the leaflets whichoccurs upon the reversal of blood flow causes prompt pivoting of theleaflets toward the closed positions.

U.S. Pat. No. 5,152,785 (Oct. 6, 1992) and U.S. No. 5,192,309 (Mar. 9,1993) show heart valves which are generally similar to that lastmentioned. The '309 patent illustrates valves having an alternativeconstruction wherein inclined camming surfaces are provided onprojections located at the upstream edge of the valve body, which areengaged by the upstream edges of the respective leaflets to create acamming action. Guidance for determining the path of the leaflets isalso provided by cylindrical lateral ears that translate in slots formedin flat sidewall portions of the valve body.

U.S. Pat. No. 5,350,421 (Sep. 27, 1994) is similar to the '309 patentand specifically illustrates a construction that is responsible forprerotation of the leaflets occurring at the end of the downstream flowof blood through the valve just prior to its reversal.

U.S. Pat. No. 5,314,467 (May 24, 1994) discloses a bileaflet heart valvewherein leaflets of composite curvature are supported by laterallyextending elongated ears which are received in recesses formed indiametrically opposed flat wall sections of the interior surface of avalve body that is formed with a flared outflow seat region againstwhich the leaflet downstream edges seat. The recesses each have aserpentine guide wall along the upstream edge thereof. The combinationof it and a second downstream wall creates a sequence of rotational andthen translational movement of the leaflets as they pivot from the openposition to the closed position.

More recently, attention has also begun to be given to trileafletvalves, and the study of blood flow through such multiple leaflet valveshas convinced many investigators that it is very important that emphasisshould be given to achieving designs with minimum turbulence and minimumpressure drop. It was generally believed that the shorter the axiallength of a valve body was, the less would be the resistance to bloodflow through the critical region of the valve, because the valve bodywas of course the region of greatest constriction. Many patented valvedesigns also concentrated on the shape and the placement of theoccluders to minimize pressure drop and turbulence.

A number of U.S. patents, such as U.S. Pat. Nos. 4,363,142, 4,328,592,5,178,632 and 5,171,623 illustrate heart valves having relatively shortvalve bodies of generally circular cross-section, some of which haverounded or radially outwardly flared upstream and downstream ends. U.S.Pat. No. 5,078,739 shows a heart valve having a sloping entrance endwherein the leaflets are mounted external of the valve body viaresilient hinges embedded in the downstream end surface of the valvebody. U.S. Pat. No. 4,775,378 shows a heart valve having a singleoccluder with a shallow S-shaped curvature that is alleged to promotethe formation of a stable closed vortex on the suction side of theoccluder; it is employed in combination with a valve body having acircular cross-section passageway that is continuously and increasinglyconstricted, i.e. its diameter decreasing, in the downstream direction.U.S. Pat. No. 4,846,830 discloses a bileaflet valve having a similarvalve body wherein a pair of curved leaflets are employed which arearranged to create a venturi tube nozzle in the direction of downstreamflow which is alleged to avoid vortex formation. U.S. Pat. No. 4,995,881shows a valve having a similarly sloping entrance in combination with apair of leaflets that are curved in the downstream direction so as todefine a nozzle-shaped passage centrally between the two leaflets whenthey are in their open position orientation.

The more that such mechanical prosthetic valves have been studied, themore that investigators have concluded that the ideal prosthetic valvesimply does not yet exist. From a materials standpoint, pyrolytic carbonhas been determined to be adequately nonthrombogenic; as a result, theproblem of combatting thrombosis in mechanical valves is presently feltto lie in preventing excess turbulence, high shear stresses and localregions of stasis. Blood is a very delicate tissue, and even minorabuses caused by turbulence and high shear stress can cause eitherthrombosis or emboli generation at local regions of stagnation.Therefore, it is felt that future improvement in the characteristic ofthromboresistance in mechanical valves will likely be attained throughthe achievement of smooth, nonturbulent flow and the absence of stasis.

The search continues for improved mechanical heart valve prostheses thatprovide passageways through which blood will flow freely and with aminimum of drag in the open position, which will close quickly upon theoccurrence of backflow to minimize regurgitation of blood, and which canbe efficiently manufactured and assembled. Accordingly, new valvedesigns incorporating such features have continued to be sought.

SUMMARY OF THE INVENTION

The present invention provides bileaflet mechanical heart valveprostheses having the aforementioned desirable characteristics whereinleaflets can assume an orientation in the open position where they areparallel to the longitudinal axis of the valve passageway but will stillpromptly close, with guidance and control of the leaflets beingaccomplished solely by contact between laterally protruding ears andcomplementary-shaped cavities in the sidewalls of the valve body inwhich they are received which have straight camming edges that areangularly located to achieve prompt pivoting, thus easing manufacturingrequirements because the most critical tolerances to be maintained aresubstantially confined to a single region of the valve body.

Because turbulence in mechanical heart valves can damage blood and leadto clotting, such sources which exist both at the leading edges ofleaflets that are inclined to the direction of blood flow and at theleading edge of the valve body orifice itself should be taken intoconsideration. When a liquid must pass around a corner, as when enteringan orifice, separation occurs, and turbulence and elevated shearstresses are created in such zone of separation. By selecting a valvebody of relatively extended axial length, by mounting leaflets thereinso that, in their open orientation, the leaflets are individually freeto generally follow blood flow and orient themselves so as to beparallel to the direction of downstream blood flow at any instant (tominimize the turbulence associated with the leaflets), and by alsocontouring the orifice inlet to eliminate that usual zone of separationthat would otherwise be present, both head or pressure loss and thetendency for thrombosis generation are concomitantly decreased.

The leaflets preferably have rectilinear surfaces that will assume anorientation in alignment with the instantaneous direction of blood flowin the full open position, such as substantially parallel to thecenterline through the valve, e.g. about 2° or less therefrom, therebyminimizing resistance to the downstream flow of blood; such rectilinearleaflet surfaces can be flat or cylindrical. The leaflets should beparallel when blood flow is at its highest level; however, when thevelocity of the downstream blood flow slows near the end of the pumpingstroke, they may undergo a prerotation toward their closed orientationfrom such parallel orientation.

More specifically, it has been found that the entrance at the upstreamend of the valve body should be essentially a section of a torus havinga radius of curvature which is at least about 28% of the radius of thecentral passageway through the valve body and not greater than about80%, that the valve body should have an average axial length at leastabout equal to the central passageway radius, and that the flaringtoroidal entrance section should extend circumferentially about theopening but preferably does not extend axially a distance greater thanabout one-third of the average axial length of the valve body.Preferably the surface is at least about 30% of a quadrant of a toruswhich at its downstream end is preferably tangent to the remainder ofthe interior surface, which is preferably generally cylindrical.

Because the flow through such a valve body has been found to be afunction of the fourth power of its diameter, the diameter of thepassageway through such a valve body is maximized by using the thinnestvalve body wall that is structurally adequate, in addition having theaverage axial length of the valve body be equal to at least about theradius of the interior cross-section. The interior diameter ispreferably advantageously maximized by allowing the exterior surface ofthe valve body to interface directly with the tissue annulus from whichthe natural valve has been excised, and suture rings are preferablyemployed which permit both mitral valves and aortic valves to be solocated that the raw tissue annulus interfaces directly with thepyrocarbon outer surface of the valve body. The mitral valve suture ringmay be a fairly straightforward design; however, for a replacementaortic valve, a suture ring is designed to permit the valve to belocated above the aortic annulus in a location so that its upstreamflared entrance will be slipped into the aortic orifice region so thatits outer wall surface interfaces directly with the tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bileaflet heart valve embodyingvarious features of the present invention, shown with the leaflets inthe open position.

FIG. 2 is a sectional view taken generally along the line 2--2 of FIG. 1showing the leaflets in the full open position, and with a suture ringattached to the valve body.

FIG. 2A is a sectional view taken generally along the line 2--2 of FIG.1 showing the leaflets in the full open position, and with analternative suture ring attached to the valve body.

FIG. 3 is a view similar to FIG. 2 showing the leaflets in theirprerotation orientation as they would be when the downstream flow ofblood slows prior to reversal.

FIG. 3A is a fragmentary sectional view taken along the lines 3A--3A ofFIG. 3.

FIG. 4 is a view similar to FIG. 2, showing the leaflets in elevationand in their closed position, with the suture ring omitted.

FIG. 5 is a plan view looking downward at the valve shown in FIGS. 1 and2 with the leaflets in the full open position.

FIG. 6 is a vertical sectional view through the valve taken generallyalong the line 6--6 of FIG. 2 with the leaflet in the full openposition.

FIG. 7 is a perspective view of a leaflet from the valve of FIG. 1.

FIG. 8 is a side elevation view, reduced in size, of the leaflet of FIG.7.

FIG. 9 is a front view of the leaflet of FIG. 8.

FIG. 10 is a fragmentary sectional view, enlarged in size, takengenerally along the line 10--10 of FIGS. 5 and 6 with the sewing ringremoved, showing the location of the ear in the cavity in the valve bodysidewall when the leaflet is in its full open position.

FIGS. 10A through 10D are full sectional views similar to FIG. 10 withthe right-hand leaflet omitted and with the left-hand leaflet shownrespectively (A) in the prerotation position, (B) at the beginning ofclosing movement, (C) in an intermediate position during closingmovement and (D) in its full closed position.

FIGS. 11 and 12 are fragmentary horizontal sectional views takenrespectively along the lines 11--11 and 12--12 of FIG. 3, with theleaflets removed.

FIG. 13 is a fragmentary sectional view taken generally along the line13--13 of FIG. 2A.

FIG. 14 is a fragmentary sectional view, enlarged in size, illustratingthe valve body wall structure.

FIG. 15 is a view similar to FIG. 14 showing the aortic sewing ringattached.

FIG. 16 is a sectional view similar to FIG. 2 of an alternativeembodiment of a bileaflet heart valve embodying various features of theinvention shown with the leaflets in the open position and with a suturering attached that is designed to facilitate mounting of the valve inthe aortic position.

FIG. 17 is a vertical sectional view taken through the valve and throughone of the leaflets along the line 17--17 of FIG. 16.

FIGS. 18A through 18D are sectional views similar to FIGS. 10A through10D with the right-hand leaflet omitted to show the details of thecavities, which details are omitted from each left-hand cavity, and withthe section through the leaflet ear showing the left-hand leaflet,respectively, (A) in the fully open position, (B) at the beginning ofclosing movement, (C) in an intermediate position during closingmovement, and (D) in the fully closed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated in FIG. 1 is a prosthetic heart valve 11 constructed so asto embody various features of the present invention. Very generally,heart valves having this construction have improved flowcharacteristics, particularly when the valve is in its fully openposition, because the leaflets can align parallel to the valvecenterline or can align at slight deviations thereto depending uponinstantaneous variations in the blood flow path through the valve,whichever is the low energy orientation. As a result, these orientationsminimize the resistance to blood flow and substantially reduce boundarylayer separation along major surfaces of the leaflets. The valve designalso provides good washing characteristics which guard against theoccurrence of stagnation and potential clotting. Importantly, althoughheart valves of this design exhibit a rapid response to changes in thedirection of blood, both in respect of opening and closing, the finalmovement of the closing leaflets is one almost solely of rotation sothat there is relatively low wear due to the leaflet rubbing against afulcrum within the valve body at about the time of complete closing,thus eliminating potential problems which could result from the creationof regions of substantial wear on the leaflet and on the fulcrum bytranslation movement during the final closing phase when the pressureacross the valve is building to the maximum value.

Heart valve 11 includes a generally annular valve body 13 which carriesa pair of pivoting occluders or leaflets 15 that alternately open andclose either to allow the smooth flow of blood in the downstreamdirection, as indicated by the arrow A in FIG. 2, or to prevent anysubstantial backflow of blood, i.e. regurgitation. The valve body 13defines a blood flow passageway in the form of its generally arcuate,mostly cylindrical interior wall surface 17. The valve body 13 has acurved entrance region 19 at its upstream end, which has been found tosubstantially increase streamlined flow characteristics through thevalve with low turbulence and substantially no generation of thrombosis.The details of the curved entrance region 19 which extends axially for adistance not greater than about one-third of the average axial length ofthe valve body are discussed hereinafter along with the operation of thevalve. A pair of diametrically opposed, thickened wall sections 21, asbest seen in FIG. 5, protrude inward from an otherwise right circularcylindrical surface, creating what is referred to as a tabulatedcylindrical surface as a result of the thickened sections 21 terminatingin facing, parallel flat wall surfaces 23 in which pairs of cavities orrecesses 25 are formed that function as one-half of the pivotarrangement which controls the opening and closing movements of theleaflets 15. Thus, the interior surface downstream of the curvedentrance region 19 is generally rectilinear.

The valve body 13 preferably has a scalloped downstream profile so thatthere are, in effect, a pair of shallow notches 27 formed in the contourof the valve body 13 in the regions just downstream of the thickenedwall sections 21. In a bileaflet valve of this type, the side openingsprovided by these notches 27 are aligned with the central passagewaybetween the leaflets 15 so that, upon reversal of blood flow,backflowing blood laterally enters the valve body through these sideopenings directing a surge of blood flow into the central passagewayregion and creating forces which impinge upon the leaflet outflowsurfaces, the effect of which is to further enhance prompt pivoting ofthe eccentrically mounted leaflets toward their closed positionorientations. This function is described in greater detail in U.S. Pat.No. 5,308,361, the disclosure of which is incorporated herein byreference.

The exterior surface of the relatively thin valve body 13 in the regiondownstream of the flared entrance section 19 is substantially that of asurface of a right circular cylinder except for a slightly thickenedcentral portion wherein a shallow groove 29 is formed between a pair ofraised bands 29a. A metal stiffening attachment ring 30 of unique design(FIG. 2) which is formed with a plurality of circumferentially spacedapart inwardly protruding fingers 30a is mated therewith to addstability and rigidity to the valve body. The valve body itself ispreferably made of a suitable material, such as pyrocarbon orpyrocarbon-coated graphite, as is well known in this art, which hassufficient resiliency that it can be deformed so as to permit theinsertion of the pair of leaflets 15 in their operative locations. Themetal ring 30 is also used to support the sewing ring of appropriatedesign, as broadly known in this art. Detailed examples of sewing orsuture rings which can be employed are described in U.S. Pat. Nos.4,535,483 and 5,178,633, the disclosures of which are incorporatedherein by reference.

The thickened exterior bands 29a are strategically located in thedownstream cylindrical section of the valve body spaced from the flaredentrance section 19. As explained hereinafter in detail, the shallowgroove 29 is located to accommodate the inwardly protruding fingers 30aof the metal ring 30 in either orientation as explained hereinafter. Thegroove 29, which is of arcuate cross section and constitutes thenarrowest diameter on the exterior surface is located so that it iscompletely downstream of the fulcrums which are formed in recesses 25.This arrangement permits the suture rings to be accommodated in alocation where the remaining tissue annulus will be in contact with aportion of the right circular cylindrical exterior surface of the valvebody.

The leaflets 15 are preferably identical in shape and size. Each leaflethas two rectilinear, preferably flat, surfaces, i.e. an inflow surface31 and an outflow surface 33, and the leaflet is preferably ofsubstantially constant thickness such that the surfaces 31 and 33 areparallel to each other. The inflow surface 31 is arbitrarily defined asthe surface which faces upstream with the leaflets in the closedposition (see FIG. 4), whereas the outflow surface 33 faces downstream.Although the leaflets 15 are preferably flat, other configurations, suchas sections of hollow cylinders of circular or elliptical cross section,can alternatively be employed, as discussed in more detail in U.S. Pat.No. 5,246,453, the disclosure of which is incorporated herein byreference.

The leaflets 15 each have a major arcuate edge surface 35, which islocated at the downstream edge of the leaflet in the open position, andeach has a minor mating edge surface 37 which is located at theopposite, upstream edge of the leaflet in the open position. The arcuateedge surface 35 preferably has a configuration such as to abut and seatclosely against the cylindrical sidewall interior surface 17 of thevalve body in the closed position. The minor edge surface 37 ispreferably flat and formed at an angle so as to mate flush against thecorresponding mating edge surface 37 of the opposing leaflet in theclosed position, as best seen in FIG. 4. As a result, the minor edgesurface 37 is accordingly oriented at an angle to the inflow surface 31which is substantially the same as the downstream angle which theoutflow surface 33 forms with the centerline plane in the closedposition, and it is preferably an angle between about 30° and about 60°.The centerline plane is defined as a plane which includes the centerlineof the passageway and which is parallel to the pivot axes of theleaflets; in the illustrated embodiment, it is perpendicular to the flatwall surfaces 23 of the valve body passageway. The angle in questiondefines the extent of the angular rotation that each leaflet 15 willundergo in moving from the fully open position to the fully closedposition. This is taken into consideration because there may be anadvantage in having a smaller angle, as opposed to a larger angle,because the leaflets need not rotate as great an angular distance inorder to reach the fully closed position. As illustrated in FIG. 4, thisangle is about 50° in the preferred embodiment.

As best seen in FIG. 7, the leaflets 15 each have a pair of intermediatestraight edge regions 39 located between the minor mating edge surface37 and the major arcuate edge surface 35 wherein a pair of laterallyextending ears or tabs 41 are located. As can be seen in FIG. 8, theears 41 are the same thickness as the flat leaflets 15 from which theylaterally extend. The ears 41 are elongated in an upstream-downstreamdirection when viewed in their open orientation. FIGS. 7 and 9 show thatthe ears 41 have lateral edge surfaces which are rectilinear surfaces ofgenerally shallow curvature as viewed looking at the leaflet from theinflow surface 31. More specifically, as best seen in FIG. 7, they eachhave a shallow rounded upstream edge surface 43 and a generally similardownstream edge surface 45. The upstream edge surface 43 is the longer,extending generally laterally of the ear, and it meets and blendssmoothly into the downstream surface 45. The major portion of therectilinear upstream edge surface 43 is perpendicular to the flat inflowand outflow surfaces of the leaflets 15, which flat surfaces simplyextend through the regions of the ears, so that the ears have inflow andoutflow surfaces that are coplanar with the leaflet main body inflow andoutflow surfaces 31, 33. A short arcuate transition edge section 47 isinterposed between the major arcuate edge surface 35 and the flatsection 39.

As previously mentioned, the valve body 13 is formed with the thickenedwall sections 21 in the regions where the cavities 25 are located, andpreferably these thickened sections are formed with flaring transitionsurfaces, i.e. an upstream transition surface 49 and a downstreamtransition surface 51 which lead smoothly from the circular entranceregion and the circular exit region of the valve body to the flat wallsurfaces 23 wherein the cavities 25 are located. A surface such as thesurface 49 may be referred to as a radial swept surface. As a result,the flow passageway through the valve body is generally circular incross-section except for the two thickened sections 21 which extendinward to the flat wall surfaces 23. As previously indicated, the planecontaining the centerline axis of the generally circular passageway thatis oriented perpendicular to the flat surfaces 23 is referred to as thecenterline plane and is frequently used for reference purposesthroughout this specification.

The arrangement is such that each thickened section includes twoside-by-side cavities which are mirror images of each other and whichare located on opposite sides of this centerline plane. As seen in FIGS.12 and 13, the cavities 25 each have a curved sidewall region 53surrounding a central flat rear section 54; however, the depth of thecavities 25 is such that the apex of the curved upstream edge surface 43of the ear does not quite touch the rear walls 54 of the cavities, e.g.a clearance of about 1-4 mils (0.001-0.004 inch). The flat wall surfaces23 of the thickened regions serve as the primary bearing surfacesagainst which one or the other of the straight edge surfaces 39 of theleaflets will usually bear whenever the leaflet is moving between itsopen and the closed positions. The clearance between the shallow curvededge surface 43 of the ear and the rear wall of the cavity is such tofacilitate a controlled cleansing spurt of blood flow, upstream throughthe cavity past the leaflet ears during the moment of complete closureof the valve as shown in FIG. 4; this guards against the possibility ofthe occurrence of clotting in the pivot region. The proportioning of theears 41 and the cavities is such that this cleaning leak is not a highvelocity jet that might cause hemolysis; instead, it is a controlledflow through a long narrow leak path that does not induce thrombosis.

As best seen perhaps in FIG. 10, the cavities 25 are formed to have anupstream lobe 57 and a downstream lobe 59 on opposite sides of anintermediate throat section 61. The intermediate throat section isformed by a pair of curved fulcrums termed an outward fulcrum 63 and aninward fulcrum 65 with respect to their location having reference to thecenterline plane. The outward fulcrum 63 is located substantially evenwith, but preferably slightly upstream of said inward fulcrum.

The upstream lobe 57 is formed with an inclined, straight, camming wallsection 67, which is oriented at an angle of between about 5° and about30° to the centerline plane and preferably between about 15° and about25°. Although the camming wall section 67 is part of the peripheral wallregion 53 and thus has curvature in a radial direction, it issubstantially rectilinear and is thus referred to as being straight. Atits upstream end, the camming wall section joins a concavely curved wallsection 69, which leads gradually downstream from this junction pointand serves a guidance function that is described hereinafter.

The downstream lobe 59 includes a flat locator wall section 71immediately below the inward fulcrum, at the downstream end of whichwall there is a downstream sloping section 73 leading from its junctionpoint to the downstream end 75 of the cavity. The flat wall section 71is oriented parallel to the centerline plane and thus provides a guidesurface against which the outflow surfaces of the ears 41 bear in thefull open position, as best seen in FIGS. 2 and 9. As best seen in FIG.8, the leaflet ears 41 preferably have their rounded downstream edgesurfaces 45 oriented so as to be at an acute angle to the outflowsurface 33 of the leaflet, thus presenting essentially a line of contactbetween the ear downstream edge surface 45 and the sloping wall section73, which tends to reduce friction and promote cleansing in this region.

The leaflets 15 are installed in the valve body 13 by squeezing the bodyat diametrically opposite locations, as for example along a diameterwhich is perpendicular to the centerline plane. Such deformation of theheart valve body 13 can take place in accordance with the teachings ofU.S. Pat. No. 5,336,259, issued Aug. 9, 1994, the disclosure of which isincorporated herein by reference. Squeezing causes the diametricallyopposed flat wall sections 23 to separate farther from each other topermit the leaflets to be fitted into the valve body, with the ears 41being received in the cavities 25. When the squeezing force is removed,the valve body 13 returns to its original annular configuration, leavingonly the desired minimal clearance between the flat wall surfaces 23 ofthe valve body and the straight lateral edge surfaces 39 of theleaflets, in which positions the leaflets are slidably-pivotally mountedfor travel between the open and closed positions. The metal stabilizingring 30 can be appropriately installed, as by snapping into place or byshrink-fitting, in the exterior circumferential groove 29 following theinstallation of the leaflets; however, it may be preferred to installthe metal stabilizing ring before installing the leaflets. Pyrocarbon isthe preferred material of valve body construction, and compressive forceapplied to a pyrocarbon structure by such a metal ring can improve thestructural properties of a pyrocarbon valve body. Such a metal ring willbe chosen which will have sufficient resiliency to return to itsperfectly annular shape following removal of such a squeezing force.

By designing the thickened bands 29a so that an inclined ramp is formedat the downstream edge of the downstream one of the two bands, it ispossible to install the metal ring 30 by sliding it upward from thedownstream end of the valve body 13 and allowing the fingers 30a to snapinto place; however, it should be understood that the ring could beinstalled by shrink-fitting if desired.

The irregular ring 30 is shaped so that a section having an inwardlyarcuate cross section is received in the arcuate cross section grooveand the adjacent section having an inwardly cylindrical surface isseated snugly upon one of the two raised bands 29a that flank the groove29, depending upon whether a mitral or an aortic sewing ring is to beinstalled. The unique stiffening ring 30 is designed to facilitate theinstallation of either an aortic sewing ring or a mitral sewing ringexterior of the valve body 13, as best seen by comparing FIGS. 2 and 2A.In FIG. 2, an aortic sewing ring 81 is illustrated which is designed toleave the upstream exterior surface of the valve body free and clear topermit its insertion into the aortic annulus from which the defectivenatural valve was excised. For this installation, the irregularstiffening ring 30 is slid onto the valve body 13 from the downstreamend with the smaller section having the arcuate, radially inwardprojections leading. Each of the projections are connected by a thinneck section to the main portion of the stiffening ring as best seen inFIGS. 3 and 3A, which has a cylindrical radially interior face. When theleading projections reach the downstream band 29a flanking the groove29, sufficient deflection occurs for the ring to continue its upstreamtravel until the groove is reached, into which the projections then snapin place, as seen in FIG. 6, with the main portion of the stiffeningring tightly surrounding the downstream cylindrical band 29a of thevalve body and preferably placing it in at least slight compression.

When the valve body is to be equipped with a mitral sewing ring 83 asdepicted in FIG. 2A, such sewing ring is positioned so as to occupy amajor portion of the exterior wall surface of the valve body 13 upstreamof the groove 29, leaving the downstream section free for insertion intothe tissue annulus from which the defective natural valve was excised.For this sewing ring, the stiffening ring 30 is installed with theopposite orientation, being slid upward from the downstream end of thevalve body 13 with the larger section of the ring 30 having thecylindrical radially interior surface leading. When it reaches thedownstream band 29a, it can be forced upstream therepast, and thearcuate inward-facing surfaces of the projections again slide over thedownstream band 29a as a result of the combined deflection which occurs.The projections again snap in place in the groove 29, but in thisinstance the major section of the ring 30 is seated tightly about theupstream band 29a, as shown in FIGS. 2A and 13.

The depth of the shallow groove 29 is such that the thickness T₂ (FIG.14) at the location of the groove is equal to at least about 85% of thethickness T₁ of the major cylindrical section of the valve body. Thethickness T₃ at the location of the bands 29a need not be greater thanabout 120% of the thickness T₁. This strategic spacing and proportioningin a valve body 13 of the present design allows the wall thickness ofthe major portion of the valve body to be minimized, thus allowing alarger diameter opening for the passageway through the valve body.Generally, it is now felt that this interior diameter of the valveshould be as large as tolerable (while still providing adequatestructural strength) because the pressure loss through the valveincreases relative to the fourth power of the diameter. Of course, eachheart valve excised from the heart of a particular patient will varywith each patient, and therefore a surgeon should have available a setof prosthetic valves of different sizes generally ranging in exteriordiameter from about 19 millimeters to 33 millimeters in diameter forfully grown adults. The reference measurement is that of the tissueannulus remaining after the defective natural valve has been excised.

The present valve design is such that it can be effectively installed sothat the tissue annulus is in direct contact with the outer surface ofthe valve body 13 for valves that are installed both in the aorticposition and in the mitral position. In this respect, it should beunderstood that, when installed, the tissue annulus of the patient willbe in contact with the exterior surface of the valve body in the regionsmarked "A" in FIGS. 2 and 2A. One result of this arrangement is evidentfrom FIG. 2A where it can be seen that the diameter of the substantiallycircular passageway through the valve is a very large percentage of thediameter of the tissue annulus, which is made possible because of therelative thinness of the major portion of the valve body wall,particularly in the region of the tissue annulus.

Alternatively, as indicated above the ring can be heated and shrink-fitonto the valve body so that the main body of the ring 30 is in contactwith the desired band 29a. Such shrink-fitting allows greatercompressive force to be applied to a pyrocarbon structure by such ametal ring and can improve the structural properties of the pyrocarbonwhich, as indicated above, is the preferred material of construction. Ofcourse, if the ring is to be installed prior to the installation of theleaflets, a metal is chosen which has sufficient resiliency to return toits perfectly annular shape following removal of the squeezing force.

With the heart valve operatively installed in a patient, when it is inthe open position, the two leaflets 15 assume an open equilibriumposition with respect to the high flow and the direction of blooddownstream through the passageway, which may be an orientation wherethey are substantially parallel to the centerline plane, as illustratedin FIGS. 2 and 2A. The location of the ear 41 within the cavity isillustrated in FIG. 10, from which it should be apparent that, shouldthe dynamic blood forces within the valve body passageway change, theleft-hand leaflet which is shown can rotate slightly clockwise so as tomaintain such a low energy position either with or without some slighttranslation. In such an equilibrium position, the leaflets 15 providevery low obstruction to the downstream flow of blood. Yet, despite evensuch a substantially parallel, full open position, the pivotconstruction is such that any translational movement either downstreamor upstream from this substantially parallel position causes theleaflets to rotate in the direction of closing. Furthermore, in thefully open position as shown in FIG. 2, the leaflets 15 are mounted soas to divide the valve body passageway into 3 sections, a center sectionlocated between the two leaflets 15 and two flanking sections. As bestseen in FIG. 5, the arrangement is such that the cross-sectional area ofeach of the two flanking passageway sections is preferably at least aslarge as the cross-sectional area of the center flow passageway section.

As previously indicated, the combination of this particular support ofthe leaflets 15, together with the shape and proportioning of the valvebody 13 contributes to the achievement of smooth nonturbulent flow andthe absence of stasis. The toroidal curvature of the curved entrance end19 leading to a generally cylindrical valve body of substantial overallaxial length has been found to achieve this desired end. Morespecifically, the construction of a valve body to have a curved entrancetransition to a tabulated cylindrical, elongated passageway has beenfound to provide very low pressure drop for a passageway of a particulardiameter. The average axial length of the valve is preferably at least50% of the interior diameter thereof. The entrance section shouldconstitute not more than about one-third of the average axial length ofthe valve body, and it should smoothly join with the downstream section,preferably being tangent thereto. The entrance section is preferablyessentially a section of the surface of a torus. The torus is selectedso that the interior diameter of the torus is between 80% and 120% ofthe diameter of the interior circular cross-section of the passagewaythrough the valve body, and preferably between about 90% and 100%. Mostpreferably it is about 100% so that it will be substantially tangent tothe right circular cylindrical downstream interior surface; if not, ashort transition section is included. The radius of curvature of thecircle that is revolved to create the torus is between about 28% andabout 80% of the radius of the valve body and preferably between about40% and about 65%. In FIG. 14, the interior radius of the valve body ismarked "R₁ ", and the radius of curvature of the torus is marked "R₂ ".To facilitate aortic installation, the exterior diameter D_(E) at theentrance end 19 should not be more than about 10% greater than theexterior diameter D_(V) of the major cylindrical outer surface of thevalve body; preferably, it is about 6-7% greater. By locating thestiffening attachment ring at a location in the valve body that isdownstream of the pivot axes of the leaflets, i.e. downstream of thefulcrums where the contact for pivoting is defined, it can accommodatesuture rings designed to have the tissue annulus directly lie in contactwith the exterior surface of the valve body either upstream ordownstream of such suture ring in the regions A in FIGS. 2 and 2A. Suchan arrangement contributes to a thinner wall thickness and a largerinterior diameter for the passageway.

During conditions of high rate of flow of blood downstream through thevalve body, both leaflets 15 can be oriented substantially parallel tothe centerline of the valve with the outflow surfaces of the ears 41 incontact with the flat wall sections 71 of the downstream lobes of thecavities 25 and with the ear upstream edge in juxtaposition with thecamming wall 67 so that rotation past the parallel orientation isprohibited. The flow rate of blood through the valve during the pumpingstroke of the associated chamber of the heart will generally exertsufficient force upon the inflow surfaces 31 of the leaflets such as tomaintain the leaflets in this substantially parallel alignment. However,when the peak downstream flow of blood has passed so that it slows inits approach to zero flow, prior to the beginning of the reverse flowcycle, the forces of the flowing bloodstream tending to orient theleaflets in such a parallel position lessen, and as a result, the dragof the bloodstream against all of the surfaces of the leaflet becomesthe predominant force. This net force tends to move the leaflets and theears 41 slightly farther downstream, which is permitted by the contourof the downstream lobes 59. However, such further downstream leafletmovement is guided by the engagement of the outflow surface edges of thedownstream ear surfaces 45 along the sloping sections 73 of the cavityand the inward fulcrums 65. The result of the ears 41 shifting to suchdownstream positions, as shown in FIG. 10A, is that the leaflets are nolonger parallel to the centerline; instead, they have rotated slightlytoward the closed orientation, i.e. so that they are now preferably atan angle to the centerline of about 2° to about 5°, and preferably 3° orgreater, as depicted in FIG. 3. This prerotation of the leaflets 15occurs near the end of pumping stroke and reduces the amount ofregurgitation, i.e. the volume of blood which will pass upstream throughsuch prosthetic heart valve prior to the occluders next reaching theirfully closed position orientations, on the next closing. This reductionoccurs for the following two reasons: (a) the leaflets now need to pivota fewer number of angular degrees to reach the closed position by reasonof the headstart they have from the substantially parallel orientationand (b) the backflowing blood has the immediate opportunity topreferentially contact the leaflet outflow surfaces 33, as opposed tothe inflow surfaces 31, so that this component of the overall forcesbeing applied to the leaflets during closing is increased.

More specifically, as the reverse flow of blood upstream through thevalve begins, the leaflets 15 and the ears 41 immediately translateupstream. This upstream translation of the ears causes immediate cammingengagement of the inflow surface edge of each upstream edge surface 43against the adjacent straight camming wall section 67 of each cavity,while the outflow surfaces of the ears may slide along the roundedinward fulcrums 65. By camming engagement is meant contact wherein thereis relative sliding movement along a surface which is inclined to thedirection in which the net forces are attempting to move an object, i.e.upstream and parallel to the centerline of the valve body; this cammingaction causes the leaflet to very promptly pivot or swing toward itsclosed position while the translation movement continues. Accordingly,upstream translational movement of the ear in the cavity 25 assures thatthe pivoting of each leaflet toward its closed position orientationoccurs promptly at the very beginning of reverse flow and continues,driven by these forces, until the upstream edges of the leaflet earsreach the top of the upstream lobes 57, as illustrated in FIG. 10B. Suchinitial pivoting is guided by the movement of the inflow surface edge ofthe ear upstream surface 43 along the camming surface 67 while theoutflow ear surface generally slides along the inward fulcrum 65,causing such pivoting or rotation to take place about a center ofrotation of pivot that is remote, i.e. which is located substantiallypast the centerline plane of the valve body; as a result, the length ofthe moment arm acts to accelerate the initial rotational closingmovement. Very low friction is encountered because there is noengagement between the ears and the walls of the cavities such as wouldcreate a significant frictional force that would resist closing.

When the force of the backflowing blood against the outflow surface 33of each leaflet has become significant, it causes the inflow surfaces ofthe ears to contact the outward fulcrums 63, as shown in FIG. 10C, andpivoting thereafter continues guided in part by sliding contact with theoutward fulcrum 63. The leaflet has thus pivoted a significant amount asa result of the upstream translation and the shifting to contact withthe outward fulcrum 63. Thereafter, the upstream edge surfaces of theears are guided by movement along the arcuate wall section 69 while theears simultaneously engage the outward fulcrums 63. Contact with theconcave wall sections 69 and the fulcrums 63 remains substantiallycontinuous for about the final one-half of the angular rotation of theears, and the curvature of the wall 69 is designed so that substantiallyonly rotational motion occurs as the upstream edge surfaces 43 slidetherealong as the leaflets thereafter swing to the fully-closedposition, illustrated in FIG. 10D and in FIG. 4. In such position,mating edge surfaces 37 of the leaflets abut each other, and thedownstream arcuate edge surfaces 35 of the leaflets abut and seatagainst the cylindrical interior surface 17 of the valve body. During amajor portion of the closing movement and specifically during the finalstages, this motion is almost pure rotational motion to avoid sliding ofthe ears along the fulcrums at this time when the upstream edges of theears move slightly downstream as a result of this rotation. When themating edges 37 of the two leaflets meet, the contact between theupstream edge of each ear and the arcuate wall 69 is broken, as seen inFIG. 10D, thus avoiding the possibility of localized wear when thepressure across the valve is very high. When the leaflet reaches itsnearly closed position, the liquid between the edge 35 of the leafletand the orifice wall acts like a cushion, and the leaflet furtherdecelerates just before it impacts the wall, reducing the noise and anypropensity for cavitation.

In the fully closed valve with the leaflets 15 oriented as illustratedin FIG. 4 wherein they are shown in elevation, the force of the bloodagainst the outflow surface 33 of each leaflet is borne mainly by thedownstream arcuate edge surfaces 35 seating against the interior valvebody surface and by the ears 41 bearing against the outward fulcrums 63.At the instant complete closure is achieved, the pressure of the bloodagainst the outflow surfaces of the leaflets is at its highest andresults in controlled leakage through the cavities 25 in an upstreamdirection. Such leakage is around and past the ears 41 in each cavity ascan be seen from FIG. 10D and is controlled in part by the depth and thelength of the ears 41. The dimensioning of the ears and the cavitiescreates a pathway for controlled backflow laterally past the edges ofthe leaflet ears and thus tends to concentrate such leakage backflow inthe regions of the pivot arrangements where such cleansing flow servesto positively guard against the occurrence of clotting. In this respect,the average clearance between the edges of the ears 41 and the walls ofthe cavities 25 is preferably at least about 50 microns or about 0.002inch, with the clearance being the least at the region of the apex ofthe curved upstream edge surface 43. There may be slightly greaterclearance adjacent the edge surfaces 45 (FIG. 7) of the ears because ofthe translating design of the leaflets.

When blood flow again reverses, as for example when the pumping strokeof the associated chamber begins again, downstream displacement, i.e.translation, of the leaflets 15 initially occurs as a result of theforce of the blood against the inflow surfaces 31. As is evident fromFIG. 10D, the outflow surfaces of the ears 41 will quickly come incontact with the inward fulcrums 65, causing opening pivoting motion toquickly begin with the major arcuate edge surface 35 swingingdownstream. The downstream edge surfaces 45 of the ears will likelyreach the lower arcuate ends 75 of the downstream lobes 59 prior to theears rotating completely about their pivot points on the fulcrums 65;however, when the blood flow through the valve approaches maximum, thenet forces on the inflow surfaces 31 of the leaflets are such that theears will be ramped upstream along the sloping wall sections 73, causingthe leaflets to be displaced just slightly upstream until thesubstantially parallel position shown in FIG. 10 is reached, with theears abutting the flat wall section 71 in each downstream lobe.

Illustrated in FIGS. 16, 17 and 18A-18D is an alternative embodiment ofa prosthetic heart valve 111 which is constructed so as to facilitatethe leaflets aligning parallel to the valve centerline or at slightdeviations thereto depending upon instantaneous variations in the bloodflow path, whichever is the low energy orientation. The cavities areparticularly shaped so that the leaflet ears can reach such a parallelorientation initially and can move slightly away from and return to suchan orientation during blood flow through the valve for a single pumpingstroke. The heart valve 111 includes a generally annular valve body 113which is generally similar to that previously described. It is designedto function with a pair of leaflets that are exactly the same as thosepreviously described. Thus, the reference numerals 15 are used, and thedescription of the leaflets is not repeated. The valve body 113 has aninterior wall surface which includes two arcuate sections 117 thatrespectively flank two diametrically opposed flat wall sections 123, andit is likewise formed with the smoothly curved entrance region 119 atits upstream end. A pair of cavities 125 is formed in each flat wallsection 123, and shallow notches 127 formed in the downstream wallportion of the valve body provide side openings into the passageways andcreate a scalloped profile for the valve body 113.

The generally right circular cylindrical surface of the major portion ofthe exterior of the valve body 113 is interrupted by a thickened band129 which facilitates the installation of a suture ring 130. In theembodiment illustrated in FIG. 16, a suture ring 130 is schematicallydepicted of a type that would be used to mount the heart valve 111 inthe aortic position. When the valve 111 is so mounted, the tissueannulus remaining where the defective valve was excised lies in directcontact with the exterior surface of the valve body in the region markedA in FIG. 16 which constitutes a concave surface section of the interiorof a torus. It can be seen that this arrangement maximizes the openingof the valve passageway relative to the tissue annulus of the patientand thus promotes high flow rate of blood therethrough with very lowpressure drop thereacross.

The valve body 113 fairly closely resembles that hereinbefore described;it has a pair of thickened wall sections wherein the cavities 125 arelocated that are formed with flaring transition surfaces, i.e. anupstream transition surface 149 and a downstream transition surface 151.Each thickened section includes two side-by-side cavities 125 which aremirror images of each other and which are located on opposite sides ofthe centerline plane perpendicular to the flat wall sections 123. Thecavities are best seen in FIGS. 18A through 18D wherein the details ofcurvature are shown in each right-hand cavity, and omitted from eachleft-hand cavity so as not to detract from the description of themovement of the leaflet ears 41 within the cavities. As best seenperhaps in FIG. 17, each of the cavities 125 has a curved sidewallregion 153 which is peripheral to a central flat rear section 155. Thecavities are each formed with an upstream lobe 157 and a downstream lobe159 located on opposite sides of an intermediate throat section 161,which is formed by a curved outward fulcrum 163 and a curved inwardfulcrum 165.

The upstream lobe 157 is formed with an inclined, straight, camming wallsection 167 which is oriented at an angle of between about 5° and about30° to the centerline plane, and preferably between about 15° and about25° thereto. At its upstream end, the camming wall section 167 joins aconcavely curved wall section 169 which leads gradually downstream fromthis junction point and serves to guide the final swinging movement ofthe leaflets to the closed position.

The downstream lobe 159 includes a flat locator wall section 171 whichis located immediately below the inward fulcrum 165. A flat bottom wall173 extends at right angles from the downstream end of the locator wall171 in a direction outward and away from the centerline plane of thevalve body. The flat wall section 171 is oriented parallel to thecenterline plane and provides a guide surface against which the outflowsurfaces of the leaflet ears 41 abut in the full open position, as bestseen in FIGS. 16 and 18A. In this position as can be seen from FIG. 18A,the downstream edge 45 of the leaflet ear abuts the flat bottom wall 173of the cavity.

The leaflets 15 are installed in the valve body 113 and the suture ring130 thereupon as generally hereinbefore described. With the heart valve111 operatively installed for example as a replacement aortic valve in apatient, when the ventricle with which it is associated is pumping, itwill be in the open position with the two leaflets 15 assuming anequilibrium open position with respect to the high flow of blooddownstream through the passageway, as shown in FIG. 16.

As soon as reverse flow of blood upstream through the valve begins, theleaflets 15 immediately translate upstream causing the upstream edges 43of the ears to slide along the camming wall sections 167, as previouslydescribed with respect to the valve 11. This causes each leaflet to verypromptly begin to swing toward its closed position as the upstreamtranslation proceeds. Once the ears 41 reach the top of the upper lobes157, as illustrated in FIG. 18B, the leaflets will have swung away fromthe parallel orientation and have become significantly cocked or cantedto the direction of downstream blood flow, so that the force of thebackflowing blood against the outflow surface of each leaflet causes theears to shift away from the inward fulcrums 163 and abut the outwardfulcrums 163 as depicted in FIG. 18C. Thereafter, the upstream edgesurfaces of the ears 41 are guided by movement along the arcuate wallsection 169 while the inflow surfaces of the ears remain in contact withthe outward fulcrums 163 as shown in FIG. 18C. Contact of the ears 41with the concave wall sections 169 and with the outward fulcrums 163remains substantially continuous throughout about the final one-half ofthe angular closing movement, and the curvature of the wall 169 isdesigned so that substantially only rotational movement of the earsoccurs as the upstream edge surfaces 43 slide therealong during thecompletion of the leaflets swinging to the fully-closed positionillustrated in FIG. 18D. In such position, the mating edge surfaces 37of the leaflets abut each other, and the downstream arcuate edgesurfaces 35 of the leaflets are seated against the cylindrical interiorsurface 117 of the valve body 113, as previously described with respectto the closing movement in the heart valve 11.

When downstream blood flow again begins with the next pumping stroke ofthe associated ventricle, downstream translation of the leaflets 15initially occurs as a result of the force of the blood against theinflow surfaces 31. As will be evident from FIG. 18D, the outflowsurfaces of the ears 41 will quickly contact the inward fulcrums 165,causing opening pivoting motion to quickly begin, with the major arcuateedge surfaces 35 swinging downstream with some translation as the earsalso slide along the inward fulcrums 165. As a result of thistranslation, the downstream edge surfaces 45 of the ears will likelyreach the bottom flat walls 173 of the downstream lobes prior to theears rotating completely about their pivot points on the fulcrums 165;however, the flat bottom wall surfaces 173 allow the downstream edges toeasily slide therealong and move smoothly and quickly to the full openposition, where the outflow surfaces of the ears are in abutting contactwith the locator surfaces 171. If instantaneous blood flow thereafter issuch that a substantially parallel orientation is not the low energyposition, either or both of the leaflets can easily shift slightlybecause the upstream portions of the tabs are relatively looselyconstrained within the throat of the cavities between the facingfulcrums and the downstream edge is free to slide along the bottom flatwall 173. However, once such an instantaneous condition ends andstraight downstream flow again occurs, because of the flat transversedownstream bottom surface, a leaflet that was momentarily displaced canquickly return to the low energy parallel position as the downstreamedge 45 of the ear slides along the flat perpendicular bottom surface173.

By confining substantially all of the functionally engaging surfacesthat define the paths of opening and closing movement of the leaflets tothe regions of the cavities and the ears, many of the regions where itis necessary to hold very close tolerance are concentrated, therebyfacilitating both manufacturing processes and quality-control fitting-upprocedures. These advantageous results are felt to grow out of theillustrated upstream-downstream lobe design where the lobes areseparated by a narrow throat that is formed by the flanking fulcrumswhich confine the associated leaflet ear and assure smooth movement andpositive resistance to jamming. Such a design can effectively functionby the use of ears which have cross sections that are generallyelongated rectangles or trapezoids, i.e. quadrilaterals having 2parallel walls of a length at least about 3 times its thickness, in suchdouble-lobed cavities. Moreover, by limiting at least the final aboutone-third of the closing movement of the leaflets to one ofsubstantially rotation only, the likelihood of severe wear occurring atsuch points of contact, when force on the leaflet ears is at about itsmaximum, is greatly diminished.

The overall design of the valve is such that gross hemodynamics in termsof energy loss per cardiac cycle are completely acceptable and aresuperior to mechanical heart valves that are presently commerciallyavailable. Because blood is a very delicate tissue and even minor abusescaused by turbulence and high shear can result in thrombosis or emboligeneration at local regions of stagnation, it is very important thatexcessive turbulence coupled with high shear stresses and local regionsof stasis be avoided. The foregoing valve design has been found toexcellently fulfill such requirements. The employment of leaflets withrectilinear surfaces that are free to follow and easily orientthemselves substantially parallel to straight downstream blood flowminimizes the turbulence associated with the leaflets themselves. Adesired cavity design which can effect prerotation of the leaflets afterthe downstream flow through the valve has peaked and nears the end ofits cycle can often further reduce regurgitation; however, the pivotarrangement itself and the location of the side notches 27 in the valvebody that focus the inflowing blood against the outflow surfaces 33where the initial closing rotation forces are amplified aresignificantly instrumental in achieving this desired end result.

Although the invention has been described with respect to certainpreferred embodiments, which include what the inventors presentlyconsider to be the best mode for carrying out the invention, it shouldbe understood that various changes and modifications that would beobvious to one having the ordinary skill in this art may be made withoutdeparting from the scope of the invention which is defined by the claimsappended hereto. For example, as earlier indicated, the invention is notlimited to occluders in the form of leaflets having flat body sectionsbut is considered to be also applicable to leaflets having curved bodysections with substantially rectilinear surfaces. In this respect, itmay be desirable to facilitate the creation of a central passageway ofgreater area through such a bileaflet valve by employing a pair of suchcurved leaflets to achieve a different distribution of the downstreamblood flow through the valve body.

Particular features of the invention are emphasized in the claims whichfollow.

What is claimed is:
 1. A prosthetic heart valve includinga generallyannular valve body having an interior, generally arcuate wall surfacewhich defines a central passageway for blood flow therethrough which isgenerally symmetrical about a longitudinal centerline, a pair ofcooperating leaflets, each having an inflow surface and an outflowsurface, said leaflets being mounted in said valve body to alternatebetween an open position where the flow of blood in a downstreamdirection is permitted and a closed position where the flow of blood inthe reverse direction is blocked, and a pivot arrangement which guidessaid leaflets in moving between said open and closed positions andpermits said leaflets to assume an orientation substantially parallel tosaid longitudinal axis in a full open position during downstream flow ofblood, said pivot arrangement comprising two ears respectivelyprojecting laterally from opposite side edges of each said leaflet andtwo pairs of diametrically opposed cavities in said interior surface ofsaid valve body for receiving said ears, said ears each being elongatedin an upstream-downstream direction when said leaflets are in the openposition so as to have an upstream edge surface and a downstream edgesurface, said leaflets being axially displaceable in an upstreamdirection upon the reversal of blood flow from its normal downstreamdirection, and said cavities each being formed with an upstream lobe anda downstream lobe which are separated by a throat section defined byconvex outward and inward fulcrums, said upstream lobe having formedtherein a straight camming wall oriented at an angle of between about 5°and about 30° to a plane containing said centerline and said downstreamlobe having formed therein a first flat wall section substantiallyparallel to said centerline which provides a locator surface againstwhich said ear may abut so that, upon upstream axial displacement ofsaid leaflets, a camming action is exerted upon said upstream edgesurface of each said elongated ear as a result of its engagement withsaid camming wall in said respective cavity, which camming action iseffective to cause each said leaflet to immediately begin to swingtoward its closed position orientation upon said reversal of blood flow,said downstream lobe further defined by a flat bottom wall section whichis substantially perpendicular to said first flat locator wall sectionand positioned so that said ear downstream edge surface abutsthereagainst in the full open position.
 2. A prosthetic heart valveaccording to claim 1 wherein each said ear has substantially flatoutflow and inflow surfaces which are parallel to each other.
 3. Aprosthetic heart valve according to claim 2 wherein each said cavity hassaid outward fulcrum formed therein at a location downstream of saidstraight camming wall so that said inflow surface of said ear is incontact with said fulcrum as said leaflet swings to the closed position.4. A prosthetic heart valve according to claim 3 wherein said upstreamlobe of each said cavity includes a concave arcuate wall extendinggenerally in a downstream direction from an upstream end of saidstraight camming wall, against which arcuate wall said upstream edgesurface of said ear slides to guide said leaflet in its swing to theclosed position.
 5. A prosthetic heart valve according to claim 4wherein said straight camming wall and said arcuate wall are located insaid upstream lobe and said arcuate wall is shaped so that said upstreamedge of said ear swings continuously downstream during the final portionof closing movement of the leaflet which is one of substantially onlyrotation.
 6. A prosthetic heart valve according to claim 5 wherein saidleaflets have substantially rectilinear outflow and inflow surfaces thatare flat and parallel to each other.
 7. A prosthetic heart valveaccording to claim 6 wherein said leaflet ears have inflow and outflowsurfaces which are substantially coplanar with said inflow and outflowsurfaces of said leaflets, and wherein said outflow surface of said earabuts said first flat locator wall section in said downstream lobe inthe full open position.
 8. A prosthetic heart valve according to claim 7wherein said inward fulcrum is located at the upstream end of said firstflat wall section and wherein the dimension of said throat section issuch that said outflow surface of said ear is in contact with saidinward fulcrum during at least initial opening movement of said leaflet.9. A prosthetic heart valve according to claim 8 wherein said earupstream edge surface is rectilinear and substantially perpendicular tosaid flat outflow and inflow surfaces of said leaflet.
 10. A prostheticheart valve according to claim 1 wherein said valve body has an interiorsurface comprising sections of a right circular cylinder and whereineach said leaflet has a minor mating flat edge surface which abuts themating edge of the other leaflet in the closed position and has a majorarcuate edge surface which abuts said interior cylindrical wall surfaceof said valve body in the closed position, said minor mating edge beinglocated at the upstream edge of each leaflet in the open position.
 11. Aprosthetic heart valve includinga generally annular valve body having aninterior, generally arcuate wall surface that defines a centralpassageway for blood flow therethrough, which is generally symmetricalabout a longitudinal centerline and which includes two diametricallyopposed flat wall sections, a pair of cooperating leaflets, each havingan inflow surface and an outflow surface, said leaflets being mounted insaid valve body to alternate between an open position where the flow ofblood in a downstream direction is permitted and a closed position wherethe flow of blood in the reverse direction is blocked, and a pivotarrangement which guides said leaflets in moving between said open andclosed positions and facilitates said leaflets assuming an orientationsubstantially parallel to said longitudinal centerline in full openposition during downstream flow of blood, said pivot arrangementcomprising two ears respectively projecting laterally from opposite sideedges of each said leaflet and two pairs of diametrically opposedcavities in said interior surface of said valve body for receiving saidears, two of said cavities being located in each said flat wall section,said ears being elongated in an upstream-downstream direction when saidleaflets are in the open position and each having an upstream edgesurface and a downstream edge surface, said cavities permitting saidleaflets and said ears to be axially displaced upstream upon thereversal of downstream blood flow, said cavities each being formed withan upstream lobe and a downstream lobe which lobes are separated by athroat section defined by convex outward and inward fulcrums, whichlobes are spaced apart a sufficient distance so that said ear isaccommodated therebetween, said upstream lobe having formed therein astraight camming wall oriented at an angle of between about 5° and about30° to a plane containing said centerline and said downstream lobe beingdefined by a first flat wall substantially parallel to said centerlineand a flat bottom wall which is substantially perpendicular to saidfirst flat wall, and said cavities being proportioned relative to saidears so that said ears are always disposed in said throat sectionwhereby said ear in said open position lies in juxtaposition to saidfirst flat wall of said downstream lobe and said downstream edge surfacethereof abuts said flat bottom wall, and whereby, upon such upstreamaxial displacement of said leaflets, a camming action is exerted uponsaid upstream edge surface of each said ear as a result of itsengagement with said straight camming wall in said respective cavity,which camming action is effective to cause each said leaflet toimmediately begin to swing toward its closed position orientation.
 12. Aprosthetic heart valve according to claim 11 wherein each said ear hassubstantially flat outflow and inflow surfaces which are parallel toeach other.
 13. A prosthetic heart valve according to claim 12 whereinsaid upstream lobe of each said cavity includes a concave arcuate wallextending generally downstream from an upstream end of said straightcamming wall, along which arcuate wall said upstream edge surface ofsaid ear slides when said leaflet completes its swing to the closedposition.
 14. A prosthetic heart valve according to claim 13 whereineach said cavity has said outward fulcrum formed therein at a locationdownstream of said straight camming wall so that said inflow surface ofsaid ear contacts said fulcrum as said leaflet pivots to the closedposition with said upstream edge surface of said ear moving along saidconcave arcuate wall.
 15. A prosthetic heart valve according to claim 14wherein said straight camming wall and said arcuate wall are so locatedin said upstream lobe and said arcuate wall is so shaped that saidupstream edge surface of said ear swings continuously downstream duringthe final portion of closing movement of the leaflet which movement isone of substantially only rotation.
 16. A prosthetic heart valveaccording to claim 11 wherein said straight camming wall is oriented atan angle of between about 15° and about 25° to said centerline plane.17. A prosthetic heart valve includinga generally annular valve bodyhaving an interior, generally arcuate wall surface which defines acentral passageway for blood flow therethrough, which is generallysymmetrical about a longitudinal centerline and which includes twodiametrically opposed flat wall sections and flanking surfaces which aresections of a right circular cylinder, a pair of cooperating leaflets,each having a flat inflow surface, a flat outflow surface, a minormating flat edge and a major arcuate edge surface, said minor matingedges being located at the upstream edge of each leaflet in the openposition, said leaflets being mounted in said valve body to alternatebetween an open position where flow of blood in a downstream directionis permitted and a closed position where flow of blood in the reversedirection is blocked and said leaflet minor edges abut each other andsaid major edges abut said right circular cylindrical interior wallsurface sections of said valve body, and a pivot arrangement whichguides said leaflets in moving between said open and closed positionsand permits said pair of leaflets to assume an orientation substantiallyparallel to said longitudinal centerline in a full open position duringdownstream flow of blood, said pivot arrangement comprising two flatears respectively projecting laterally from opposite side edges of eachsaid leaflet and two pairs of diametrically opposed cavities in saidinterior flat wall sections of said valve body for receiving said ears,two of said cavities being located in each said flat wall section, saidflat ears being elongated in an upstream-downstream direction when saidleaflets are in the open position and each having an upstream edgesurface and a downstream edge surface, said cavities permitting saidleaflets and said ears to be axially displaced upstream, relative tosaid valve body, upon the reversal of downstream blood flow, saidcavities each being formed with an upstream lobe and a downstream lobewhich lobes are separated by a throat section defined by convex outwardand inward fulcrums which are spaced apart a sufficient distance so thatsaid flat ear is accommodated therebetween, said upstream lobe havingformed therein a straight camming wall oriented at an angle of betweenabout 5° and about 30° to a plane containing said centerline and aconcave arcuate wall extending generally downstream from an upstream endof said flat camming wall against which arcuate wall said upstream edgesurface of said ear slides when said leaflet completes its swing to theclosed position, said downstream lobe having formed therein a flatlocator wall section substantially parallel to said centerline whichflat locator wall extends downstream from said inward fulcrum and a flatbottom wall section that extends from the downstream end of said flatlocator wall at substantially a right angle thereto, and said cavitiesbeing proportioned relative to said ears so that said ears are alwaysdisposed in said throat section and so that said flat bottom wallsection facilitates sliding movement therealong of said ear downstreamsurface to allow said ear to move into juxtaposition against said flatlocator wall of said downstream lobe in said open-position duringdownstream blood flow.